1. Field of the Invention
The present invention relates to a semiconductor producing apparatus equipped with a heat treatment device such as a diffusion devices a CVD, etc., capable of heat-treating semiconductor wafers in batches, and it also relates to a temperature control method for such a semiconductor producing apparatus.
2. Description of the Related Art
In a heat treatment device for a semiconductor producing apparatus such as a diffusion device, a CVD, etc., having an electric furnace for example, it is necessary to maintain the temperature of the electric furnace at an appropriate temperature, or make the interior of the electric furnace follow a dictated temperature change. Such a temperature control is required to have high precision or high performance with respect to compensation against external disturbances, and followability against a change in a target temperature. Conventionally, a control method as illustrated in FIG. 28 for example has been used for the temperature control on such a heat treatment device.
The control method of FIG. 28 employs an adder 1 having a target temperature input end IN and outputting a deviation or diference between a target temperature inputted to the target temperature input end IN and a detected temperature (controlled quantity or variable) from a heat treatment furnace 3 to be described later, a PID adjuster in the form of a PID adjustment section 2 provided at an output side of the adder 1 for performing PID calculations (e.g., proportioning, integrating and differentiating calculations) based on an output of the adder 1 and outputting a manipulated quantity or variable for the heat treatment furnace or device 3 thus calculated, and the heat treatment furnace 3 provided at an output side of the PID adjustment section 2 and having an input end a for receiving an output of the PID adjustment season 2 as a manipulated variable and an output end h for outputting the detected temperature (controlled variable), whereby the detected temperature (controlled variable) outputted from the output end b of the heat treatment furnace 3 can be controlled to a desired value.
The PID adjustment section 2 may include, as required, a known function of coping with integration anti-wind-ups or bumpless technique. The heat treatment furnace 3 among various components of FIG. 28 is schematically configured as illustrated in FIGS. 29(a) for example. Specifically, the heat treatment furnace 3 of FIG. 29(a) includes an electric furnace 31 having an input end a for inputting a manipulated quantity or variable, an output end b for outputting a controlled variable and an introduction port through which semiconductor wafers are to be introduced or loaded into the electric furnace 31, a boat 32 for holding the semiconductor wafers in the electric furnace 31, a cap 33 for closing the introduction port of the electric furnace 31 and supporting the boat 32, a heater 34 adapted to be supplied, though not shown, with electric power in response to a control signal from the input end a to heat the interior of the electric furnace 31, and a temperature sensor 35 for detecting the temperature of the interior of the electric furnace 31 and outputting the detected temperature to the output end b, whereby the interior temperature of the electric furnace 31 is controlled to follow or maintain a specific temperature pattern, thus chemically processing the semiconductor wafers held by the boat 32.
Also, for the purpose of temperature control, the electric furnace 31 as representatively illustrated in FIGS. 20(a) and 29(b) has a heating element divided into a plurality of heating zones to each of which electric power is supplied independently of each other to control the temperature thereof. For example, in the case of FIG. 29(a), the heating element takes, if divided into four zones, such a configuration as shown in FIG. 30.
Similar to FIG. 29(a), the heat treatment furnace 3A of FIG. 30 includes, as its constructional components, an electric furnace 31, a boat 32, a cap 33 and a heater 44. The heater 44, being divided into four sections, is constructed such that it is provided with four manipulated variable input ends a1 through a4, a temperature sensor 45 for measuring the temperatures of the respective four-divided zones, and four controlled variable output ends b1 through b4 corresponding to the four zones a1 through a4, respectively.
In the following description, a collection of components provided in a route extending from the manipulated variable input end a1 to the controlled variable output end b1 may be designated at zone 1, and similarly, another collection of components in another route from a2 to b2, a further collection of components in a further route from a3 to b3 and so on may be respectively designated at zone 2, zone 3 and so on.
In the case of a heat treatment furnace of the configuration having a plurality of heating zones, for example four-divided zones as illustrated in FIG. 30, there has often been used a control scheme in which the configuration of FIG. 28 is simply formed into a plurality of heating zones in parallel with each other, as illustrated in FIG. 31. The heat treatment furnace 3A among the components of FIG. 31 has four manipulated variable input ends at through a4 and four manipulated variable output ends b1 through b4, as shown in FIG. 30. Here, reference symbols 1-1 through 1-4 designate a plurality of parallel adders, and reference symbols 2-1 through 2-4 designate a plurality of parallel PID adjustment sections.
The heat treatment furnaces as illustrated in FIGS. 30 and 31 carry out a process treatment in accordance with a temperature control procedure as shown in FIGS. 32(a) and 32(b) for example.
Here, a description will be made of an example of the process treatment carried out by such a conventional heat treatment furnace described above, while referring to FIGS. 32(a) and 32(b). FIG. 32(a) is a flowchart illustrating such an example of heat treatment carried out by the above-mentioned heat treatment furnace, and FIG. 32(b) schematically shows the temperature of the heat treatment furnace during the heat treatment. In FIG. 32(b), symbols designate processings indicated by the same symbols in FIG. 32(a).
In FIG. 32(a), a step S101 is to maintain and stabilize the temperature in the interior of the electric furnace 31 at a relatively low temperature T0. In step S101, the boat 32 has not yet been introduced into the electric furnace 31. A step 8102 is to introduce or load the boat 32 holding semiconductor wafers into the electric furnace 31. As a result of the boat 32 having been loaded into the electric furnace 31, due to the fact that the semiconductor wafers are generally lower in temperature than the temperature T0 of the electric furnace 31, the temperature of the electric furnace 31 temporally becomes lower than the temperature T0, but it is restored and stabilized to that temperature T0 in a certain period of time under the above-described temperature control.
A step S103 is to gradually raise the temperature of the electric furnace 31 from the temperature T0 to a temperature T1, which is suitable for a process treatment such as a film forming treatment on the semiconductor wafers (e.g., forming a thin layer or film on each semiconductor wafer). A step S104 is to maintain and stabilize the Interior temperature of the electric furnace 31 at the temperature T1 in order to perform a process treatment on the semiconductor wafers. A step S105 is to gradually lower, after the process treatment having been finished, the temperature of the electric furnace 31 from the temperature T1 to the relatively lower temperature T0. Thereafter, a step S106 is carried out which is to take the boat 32 holding the process-treated semiconductor wafers out of the electric furnace 31 for replacement of the process-treated wafers with new untreated wafers. All of these series of processings from step S101 to step S106 are then performed on all the untreated wafers.
When all the semiconductor wafers have been subjected to the process treatment, the series of temperature control is finished but otherwise, the semiconductor wafers on the boat having been process-treated are replaced with new untreated wafers, and the flow or process is again returned to the step S101, and the processings from step S101 to S106 are again repeated. Here, note that the processings in steps S101, S102, S104 and S106 are allowed to proceed to the following steps, respectively, after a stable state of temperature is attained in which the interior temperature of the electric furnace 31 is in a predetermined limited temperature range with respect to the target temperature and such a temperature condition continues for a predetermined period of time.
With the use of the conventional temperature control system and method as described above and illustrated in FIG. 28 or FIG. 31, however, there arises the following problem. Specifically, in the event that the target temperature rapidly changes, it becomes impossible to maintain the detected temperature (controlled variable), giving rise to a delay in the process of the controlled variable to follow the target value, as a consequence of which it takes a long time until the controlled variable reaches an allowable range with respect to the target value, thus attaining a stable state.
For example, it is necessary to finish in a short period of time the step S103 in the process treatment as illustrated in FIGS. 32(a) and 32(b) in order to enhance the time-related production efficiency of the entire heat treatment system. For this reason, it is desired to increase the rising speed of the target value, so the delay in following the target value according to the conventional temperature control system and method as referred to above becomes too great to be ignored.
In order to solve this problem, there has been known another method which is capable of improving the followability without impairing control preciseness by performing control according to a configuration as shown in FIG. 33.
The control blocks shown in FIG. 33 includes, as like components of FIG. 28, a target value input end IN, an adder 1, a PID adjustment section 2 and a heat treatment furnace 3, and as different components therefrom, a pattern generator in the form of a pattern generation section 5 for outputting, as a controlled variable for the heat treatment furnace 3, an optimal signal which is deemed suited as such, a switch in the form of a switcher 6 for selecting either one of an output of the PID adjustment section 2 and an output of the pattern generation section 5 in response to a switch control signal and outputting it as a manipulated variable, and a switch control section 7 for supervising the output of the adder 1 and outputting a switch control signal to control the switcher 6 in correspondence with a specific condition (e.g., a later-mentioned predetermined point of time, or a later-mentioned change in the output of the adder 1 exceeding a predetermined value), whereby the detected temperature (controlled variable) outputted from the output end b of the heat treatment furnace 3 is properly controlled. The pattern generation section 5 and the switch control section 7 each incorporate therein a clock timed to indicate the same time point and store a period of time from the beginning of temperature control to the time when a rapid change in the target value has occurred, from which one can know the exact time point of such a rapid change.
In the control method carried out by the control blocks shown in FIG. 33, feed-back control is carried out on the target temperature from the target input end IN and the detected temperature (controlled variable) from the output end b of the heat treatment furnace 3, which is a control target, by means of the adder 1 and the PID adjustment section 2. When an abrupt change in the target value from the target input end IN takes place, the switch control section 7 outputs a switch control signal to the switcher 6, whereby the output of the switcher 6 is switched from the PID adjustment section 2 side to the pattern generation section 5 side. As a result, open loop control is started in accordance with the output of the pattern generation section 5. At a predetermined point in time at which the output of the adder 1 again becomes nearly zero, the switch control section 7 outputs a switch control signal to the switcher 6 again, so that the output of the switcher 6 is switched over from the pattern generation section 5 side to the PID adjustment section 2 output side, thus resuming feed-back control.
More specifically, according to the control method shown in FIG. 33, when the target value has abruptly changed as in step S103 of the process treatment of FIGS. 32(a) and 32(b) for example, the switch control section 7 expects or forecasts the time point of such an abrupt change beforehand, and switches, at the expected time point, the output of the switcher 6 from the PID adjustment section 2 side to the pattern generation section 5 side, so that an optimal signal is outputted from the pattern generation section 5 at an appropriate timing, thereby temporally cutting off the feed-back loop to carry out open-loop control for improved followability. Thereafter, at a time point at which the output of the adder 1 is expected to become substantially zero, or when the output of the adder 1 actually becomes substantially zero through supervision thereof, the output of the switcher 6 can be switched to the output of the PID adjustment section 2, thus enabling the same feedback control as conventionally done.
In this connection, it is to be noted that the control method performed by the control blocks as shown in FIG. 33 can be similarly applied to another control method carried out by control blocks illustrated in FIGS. 34 and 35. Here, the control blocks of FIG. 34 further include a second PID adjustment section 12 provided at a downstream side or stage of the switcher 6 in the control blocks of FIG. 33, and a second adder 4 disposed between the switcher 6 and the second PID adjustment section 12 for feeding back a second detected temperature value (auxiliary controlled variable) to form a feed-back loop 20 for cascade control. In this case, the heat treatment furnace 3 is constructed as illustrated in FIG. 29(b), but it is further provided with a second output end c for outputting the second detected temperature value (auxiliary controlled variable) in addition to a first output end b for outputting a first detected temperature value (main controlled variable). Here, note that the first and second detected temperature values are obtained by detecting the interior temperature of the reaction tube and the temperature in the vicinity of the heater, respectively, According to this method, when the response of the heat treatment furnace 3 has changed, such a change can be alleviated by the feed-back loop 20 to enhance the control response through effective utilization of the auxiliary controlled variable, thereby improving overall control performance of the system.
Moreover, a control block configuration shown in FIG. 35 has a second adder 14 and a second PID adjustment section 15 both disposed between the pattern generation section 5 and the switcher 6 in the control blocks of FIG. 33 to form a feed-back loop 21.
With this method, a controlled variable can be outputted to the heat treatment furnace 3 while adjusting the output of the pattern generation section 5 based on the feed-back control of the second detected temperature value (auxiliary controlled variable), so that a manipulated variable can be properly and adjustably controlled based on the actual control target, thereby alleviating a change thereof, In this regard, note that the output of the pattern generation section 5 is given by outputting a recorded value stored in a memory and the like.
In cases where control is effected using the pattern generation section of the configuration as illustrated in FIGS. 33 through 35, however, it is necessary for a specific skilled engineer to repeatedly effect the process treatments as illustrated in FIGS. 32(a) and 32(b) a number of times so as to adjust the output (i.e., stored values) of the pattern generation section 5, thus requiring a lot of labor and time. Besides, such adjustments are varied depending upon the skill of the engineer, differences among individuals, etc., so control quality after adjustments varies according to the adjusting person.
In particular, in cases where a plurality of control blocks as illustrated in FIGS. 33 through 35 are connected in parallel with each other as in the control blocks of FIG. 31 comprising a plurality of control blocks as shown in FIG. 28, there arises another problem that the outputs of the plurality of pattern generation sections 5 have to be adjusted, requiring a still longer time of adjustment and further increasing variations in the controlled variable. Moreover, if the output of each pattern generation section 5 is to be obtained from the previously stored values, a further problem will arise in that a tremendous capacity of memory is required.
In view of the above, the present invention is intended to obviate the above-mentioned various problems encountered with the prior art, and has for its object to provide a novel and improved semiconductor producing apparatus and a temperature control method therefor which are capable of making a detected temperature (controlled variable) follow a target value so as to be maintained at that value even if there takes place a rapid change in the target temperature.
Another object of the present invention is to provide a novel and improved semiconductor producing apparatus and a temperature control method therefor which do not require a great memory capacity.
Bearing the above objects in mind, according to a first aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: an adjuster for receiving a target value and a detected control value through an adder; a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; and a switch for switching between an output at least including the output of the pattern generator and an output of the adjuster to generate an output.
In a preferred form of the invention, the semiconductor producing apparatus further comprises an external disturbance adjuster for receiving the target value and the detected control value through another adder and generating an output which is to be added to the output of the pattern generator so as to adjust it against an external disturbance.
Such an arrangement is achieved, for example, by adding an output of an adjuster (external disturbance adjuster 202) to an output of a pattern generation section 8E, as shown in FIGS. 23 through 26.
According to a second aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: an adjuster provided with an I adjusting section for receiving a target value and a detected control value through an adder; a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; and a switch for switching between an output including the output of the pattern generator and an output of the adjuster including the I adjusting section to generate an output.
Here, the adjuster provided with an I adjusting section is indicated by reference numerals 201, 201A in FIGS. 23 through 26.
According to a third aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: a first adjuster for receiving a target temperature value of a heat treatment furnace and a first detected temperature value from the heat treatment furnace through an adder, a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; and a switch for switching between the output of the pattern generator and an output of the first adjuster to generate an output as a manipulated variable to the heat treatment furnace.
Such an arrangement is shown, for example, in FIG. 1 in which it includes a first adjuster (PID adjustment section 2) for receiving a first detected temperature value (output at b) from a heat treatment furnace 3, a pattern generator (pattern generation section 8), and a switch (switcher 6) for switching between outputs of the first adjuster (PID adjustment section 2) and the pattern generator (pattern generation section 8).
According to a fourth aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: a first adjuster for receiving, through a first adder, a target temperature value of a heat treatment furnace and a first detected temperature value from the heat treatment furnace; a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; a switch for switching between the output of the pattern generator and an output of the first adjuster to generate an output; and a second adjuster provided at an output side of the switch for receiving, through a second adder, the output of the switch and a second detected temperature value from the heat treatment furnace and generating an output as a manipulated variable to the heat treatment furnace.
Such an arrangement is shown in FIG. 9 in which a PID adjuster (second adjuster) 12 is illustrated as receiving an output of an adder (first adder) 6 via another adder (second adder) 4 and generating an output as a manipulated variable to a heat treatment furnace 3B.
According to a fifth aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: a first adjuster for receiving, through a first adder, a target temperature value of a heat treatment furnace and a first detected temperature value from the heat treatment furnace; a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; a second adjuster for receiving, through a second adder, the output of the pattern generator and a second detected temperature value from the heat treatment furnace; and a switch for switching between an output of the second adjuster and an output of the first adjuster to generate an output as a manipulated variable to the heat treatment furnace.
Such an arrangement is shown in FIG. 19 in which the first adjuster is illustrated as a PID adjustment section 2, and the second adjuster is illustrated as a PID adjustment section 12A.
According to a sixth aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: a third adjuster provided with an I element and a fourth adjuster unprovided with an I element each for receiving, through a first adder, a target temperature value of a heat treatment furnace and a first detected temperature value from the heat treatment furnace, a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; a switch for switching between an output at least including an output of the third adjuster and a sum of the output of the pattern generator and an output of the fourth adjuster; and a second adjuster for receiving, through a second adder, the output of the switch and a second detected temperature value from the heat treatment furnace and generating a manipulated variable to the heat treatment furnace.
Such an arrangement is shown in FIG. 23 or FIG. 24, in which the third adjuster provided with an I element is illustrated as an I adjustment section 201 or a PID adjustment section 201A, and me fourth adjuster unprovided with an I element is illustrated as a PD adjustment section 202. Also, the switch is illustrated as a switcher 203 and an adder 204 in FIG. 23, and as an adder 205 and a switcher 6 in FIG. 24.
According to a seventh aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: a third adjuster provided with an I element and a fourth adjuster unprovided with an I element each for receiving, through a first adder, a target temperature value of a heat treatment furnace and a first detected temperature value from the heat treatment furnace to generate an adjuster output; a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; a second adjuster for receiving, through a second adder, a sum of an output of the fourth adjuster and the output of the pattern generator, and a second detected temperature value from the heat treatment furnace; and a switch for switching between an output of the third adjuster and an output of the second adjuster to generate an output as a manipulated variable to the heat treatment furnace.
Such an arrangement is shown in FIG. 25 in which the third adjuster is illustrated as a PID adjustment section 201A, the fourth adjuster as a PID adjustment section 202, and the second adjuster as a PID adjustment section 12E, and a switcher 6 serves to switch over between outputs of the two PID adjustment sections 12E, 201A.
According to an eighth aspect of the present invention, there is provided a semiconductor producing apparatus with a temperature control system, comprising: a third adjuster provided with an I element and a fourth adjuster unprovided with an I element each for receiving, through a first adder, a target temperature value of a heat treatment furnace and a first detected temperature value from the heat treatment furnace; a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; a switch for switching among an output of the third adjuster, a sum of an output of the fourth adjuster and the output of the pattern generator, and the output of the pattern generator, and a second adjuster for receiving, through a second adder, the output of the switch and a second detected temperature value from the heat treatment furnace and generating an output as a manipulated variable to the heat treatment furnace.
Such an arrangement is shown in FIG. 26 in which a switch (switcher 6E) serves to switch over between an output of the fourth adjuster (PD adjustment section 202), an output of a pattern generator (pattern generation section 8E), and a summed output formed of an output of the third adjuster (PID adjustment section 201A) and an output of the pattern generator (pattern generation section 8E) whereas the second adjuster (PID adjustment section 12E) outputs a manipulated variable to a heat treatment furnace 3 bas on an output of the switch (switcher 6E) and a second detected temperature value (output at c) inputted thereto via a second adder 4E.
In another preferred form of the invention, the fourth adjuster unprovided with an I element comprises a PD adjuster, and the third adjuster provided with an I element comprises an adjuster including a PID factor or a PI factor or an adjuster including an I element alone.
In a further preferred form of the invention, the first detected temperature value is an average value obtained by averaging temperature values detected at a plurality of locations of an object to be controlled with a predetermined ratio.
Such an arrangement is shown in FIG. 8 in which an averaging section 17 serves to average temperature values detected at a plurality of locations of an object (heat treatment furnace 3B) to be controlled with a predetermined ratio.
In a yet further preferred form of the invention, the semiconductor producing apparatus further comprises a parameter compensator for generating a compensation value which is used for compensating the parameters of the approximate function of the pattern generator based on the first detected temperature value.
In a still further preferred form of the invention, the parameter compensator sets an evaluation value E having a correlation with the parameters of the approximate function and evaluating whether the temperature control is good or bad, previously determines an interference matrix M (Mxc3x97xcex94P=xcex94E) representative of a relation between a minimal change xcex94P of a parameter P and a minimal change xcex94E of the evaluation value E which is caused by the minimal change xcex94P given to the parameter P, and calculates, as a parameter compensation value, such an amount of change of the parameter P as to make the evaluation value E to be a desired value by using the interference matrix M.
In a further preferred form of the invention, the semiconductor producing apparatus further comprises a parameter compensator for generating a compensation value which is used for compensating the parameters of the approximate function of the pattern generator based on the first detected temperature value, wherein the parameter compensator has an interference matrix M for calculating, as a parameter compensation value, such an amount of change in a parameter as to make the evaluation value lo be a desired value, the interference matrix having, as its factors, transfer gains each representative of a relation between a manipulated variable to the heat treatment furnace and the detected temperature value from the heat treatment furnace, whereby the parameter is compensated by the parameter compensation value thus obtained, so that the pattern generator generates a functional output by use of the compensated parameter, the switch being operable to select the output of the adjuster when a change of the target value over time is relatively limited, and the output of the pattern generator when a change in the target value over time is relatively great, so as to use it for control operation.
In a further preferred form of the invention, the semiconductor producing apparatus further comprises a parameter compensator for generating a compensation value which is used for compensating the parameters of the approximate function of the pattern generator based on the first detected temperature value; wherein the parameter compensator has an interference matrix M for calculating, as a parameter compensation value, such an amount of change in a parameter as to make an evaluation value E, which has a correlation with the parameter, to be a desired value; the interference matrix M is calculated by the following formula;
M=(Eu+Gxc3x97Kp)xe2x88x921xc3x97G
where G is a matrix having, as its factors, transfer gains each representative of a relation between a manipulated variable to the heat treatment furnace and the detected temperature value from the heat treatment furnace; and Kp is a diagonal matrix having, as its diagonal factors. constants of a P factor of the fourth adjuster inclusive of no integral factor; and Eu is an unit matrix; the parameter is compensated by the parameter compensation value thus obtained, so that the pattern generator generates a functional output by use of the compensated parameter; and the switch is operated to select the output of the adjuster when a change of the target value over time is relatively limited, and the output of the pattern generator when a change in the target value over time is relatively great, so as to use it for control operation.
In a further preferred form of the invention, upon switching of the adjuster, the output of the switch immediately after the switching is adjusted based on the output of the switch immediately before the switching, for example as shown in FIGS. 17 and 18.
In a further preferred form of the invention, when the output of the switch is switched over from the output of the first adjuster into the output of the pattern generator, the output of the pattern generator is adjusted in accordance with the output of the first adjuster immediately before the switching, for example as shown in FIG. 18.
In a further preferred form of the invention, when the output of the adjuster is switched over from the output of the first adjuster into the output of the second adjuster, the output of the pattern generator is adjusted in accordance with the output of the second detected temperature value immediately before the switching, for example as shown in FIG. 22.
In a further preferred form of the invention, the object to be controlled is a temperature in the heat treatment furnace; in a temperature control process in which the temperature in the heat treatment furnace is raised to a process temperature, the approximate function f of the pattern generator is expressed as follows;
ƒ(txe2x88x92t0, TIi, YIi, YGi, YFi)
  =                              Max          ,                                                  t            0                    ≤          t           less than                                     t              0                        +                          TI              i                                                                                              YI              i                        +                                          YG                i                            ·                              (                                  t                  -                                      t                    0                                                  )                                              ,                                                                t              0                        +                          TI              i                                ≤          t           less than                       t            2                                                        Min          ,                                                  t            2                    ≤          t                    
where t is a time variable; t0 is a start time at which the target temperature begins to rise; t2 is a time at which the function (YIi+YGixc2x7(txe2x88x92t0)) reaches YF1; and TIi, YIi, YGi and YFi are parameters.
In a further preferred form of the invention, the object to be controlled is a temperature in the heat treatment furnace; in a temperature control process in which the temperature in the heat treatment furnace is raised to a process temperature, the approximate function ƒ of the pattern generator is expressed as follows;
ƒ(txe2x88x92t0, YIi, YGi, YFi)
  =                                                        YI              i                        +                                          YG                i                            ·                              (                                  t                  -                                      t                    0                                                  )                                              ,                                                  t            0                    ≤          t           less than                       t            2                                                                    YF            i                    ,                                                  t            2                    ≤          t                    
where t is a time variable; t0 is a start time at which the target temperature begins to rise; t2 is a time at which the function (YIi+YGixc2x7(txe2x88x92t0)) reaches YFi; and YIi, YGi and YFi are parameters.
In a further preferred form of the invention, the object to be controlled is a temperature in the heat treatment furnace; in a temperature control process at the time when a boat is loaded into the heat treatment furnace, the approximate function ƒ of the pattern generator is expressed as follows;
ƒ(txe2x88x92t0, YIi, YGi)=YIi+YGixc2x7(txe2x88x92t0), t0xe2x89xa6t
where t is a time variable; t0 is a start time at which the boat begins to be loaded into the furnace; and YIi and YGi are parameters.
In a further preferred form of the invention, the object to be controlled is a temperature in the heat treatment furnace; in a temperature control process at the time when a boat is loaded into the heat treatment furnace, the approximate function ƒ of the pattern generator is expressed as follows;
ƒ(txe2x88x92t0, xcex94YIi, YGi)=xcex94YIi+YGixc2x7(txe2x88x92t0)+Y0, t0xe2x89xa6t, i=1,2 . . . , M
where t is a time variable; t0 is a start time at which the boat begins to be loaded into the furnace; xcex94YIi is a difference between YIi and Y0 upon switching; and Y0 is an output value of the first adjuster upon switching.
In a further preferred form of the invention, the object to be controlled is a temperature in the heat treatment furnace; in a temperature control process in which the temperature in the heat treatment furnace is raised to a process temperature, the approximate function of the pattern generator is expressed as follows;
ƒ(txe2x88x92t0, xcex94YIi, YGi, xcex94YFi)
  =                                                        Δ              ⁢                              xe2x80x83                            ⁢                              YI                i                                      +                                          YG                i                            ·                              (                                  t                  -                                      t                    0                                                  )                                      +                          Y              0                                ,                                                  t            0                    ≤          t           less than                       t            2                                                                                  Δ              ⁢                              xe2x80x83                            ⁢                              YF                i                                      +                          Y              0                                ,                                                  t            2                    ≤          t                    
where t is a time variable; t0 is a start time at which the target temperature begins to rise; t2 is a time at which the function (YIi+YGixc2x7(txe2x88x92t0)) reaches YF1; xcex94YIi is a difference between YIi and Y0); xcex94YFi is a difference between YFi and Y0; and Y0 is an output value of the first adjuster upon switching.
With the semiconductor producing apparatus as described above, even if there takes place an abrupt change in the target temperature value, it is possible to make the detected temperature value (controlled variable) quickly follow the target temperature value so as to be maintained at that temperature. As a result, the time-related production efficiency can be improved, and a semiconductor producing apparatus can be provided which does not require any tremendous memory capacity.
According to a ninth aspect of the present invention, there is provided a temperature control method for a semiconductor producing apparatus wherein upon determining the interference matrix, a heat treatment is carried out to obtain a first evaluation value for a prescribed evaluation item with a specified parameter being temporally set to a first value, then another heat treatment is carried out to obtain a second evaluation value for the prescribed evaluation item with the specified parameter being temporally set to a second value, and an interference matrix is previously calculated based on the temporally set first and second values and the first and second evaluation values; upon compensating the specified parameter, a third evaluation value is determined by effecting a further heat treatment after the determination of the interference matrix, so that a compensated value of the specified parameter is calculated based on a difference between the thus determined third evaluation value and a desired evaluation value using the interference matrix to thereby compensate the specified parameter, and generates, as the output of the pattern generator, a functional output using the compensated specified parameter; and upon performing temperature control, in the case where a change in the target value over time is relatively limited, the output of the adjuster is selected for use with control operation, whereas in the case where a change over time of the target value is relatively large, the output of the pattern generator is selected for use with control operation.
In a further preferred form of the invention, the compensated specified parameter is further compensated based on a difference between an actually measured evaluation value obtained upon the heat treatment using the compensated parameter and a desired evaluation value.
In a further preferred form of the invention, the pattern generation output of the function is previously calculated and stored, and the stored value is used as the output value of the pattern generator.
In a further preferred form of the invention, the output of the adjuster is selected when a change in the target value over time is relatively limited, whereas the output of the pattern generator is selected when a change in the target value over time is relatively great.
In a further preferred form of the invention, the output of at least the I adjusting section of the adjuster is selected when a change in the target value over time is relatively limited, whereas the output of the pattern generator is selected when a change in the target value over time is relatively great.
In a further preferred form of the invention, the first adjuster is provided at least with an I adjusting section; the switch is constructed so as to switch between an output including the output of the pattern generator and at least the output of the I adjusting section of the adjuster; and the output of at least the I adjusting section of the adjuster is selected when a change in the target value over time is relatively limited, whereas the output of the pattern generator is selected when a change in the target value over time is relatively great.
In a further preferred form of the invention, a parameter compensator is provided for generating a compensation value for compensating the parameters of an approximate function of the pattern generator based on the detected control value.
According to a tenth aspect of the invention, there is provided a temperature control method for a semiconductor producing apparatus including: a third adjuster provided with an I element and a fourth adjuster unprovided with an I element each for receiving, through a first adder, a target temperature value of a heat treatment furnace and a first detected temperature value from the heat treatment furnace; a pattern generator having an approximate function for calculating a pattern output and capable of changing the pattern output in accordance with parameters of the approximate function; and a switch for switching between a first output of the third adjuster, a second output in the form of a sum of an output of the fourth adjuster and the output of the pattern generator, and a third output of the pattern generator; wherein the switch is operated in such a manner that it selects the first output to carry out temperature control when a change in the target value over time is relatively limited, the second output to carry out temperature control when a change in the target value over time is relatively great, and the third output to carry out temperature control in a transient period in which a change in the target value over time transfers or shifts from a relatively great state to a relatively limited state.
In a further preferred form of the invention, the state of a change in the target value over time being relatively great is a ramp-up period, and the transient period of a change in the target value over time transferring from a relatively great state into a relatively limited state is an end point of the ramp-up period.
With the temperature control method as described above, even in the event an abrupt change takes place in the target temperature value, it is possible to make the detected temperature value (controlled variable) quickly follow the target temperature value so as to be maintained at that temperature Consequently, the time-related production efficiency can be improved, and a temperature control method can be provided which does not require any tremendous memory capacity.
According to an eleventh aspect of the invention, there is provided a method for producing a semiconductor device by using the temperature control method for a semiconductor producing apparatus as described above.